i wanna find the title of the science fiction horror movie that i saw long time ago...

in the movie, small rocks are on the beach... when some children pick it up, it attacks the face of a child... and some guy is attacked by an alien. and his upper body is literally broken off... last scene is only female survivor sitting and crying on a highway in the middle of completely deseeted city (maybe LA). what is the title of the film? thanks!